Studies of the oral actinomyces and streptococci are continuing toward defining the molecular mechanisms involved in the adherence of these bacteria to each other and to oral tissue surfaces. Adsorption of Actinomyces viscosus to salvia-treated hydroxyapatite appears to be a specific function of the organisms type 1 fimbrial component. The presence of these fimbriae may therefore contribute to the appearance of A. viscosus as an early colonizer of cleaned tooth surfaces. Lactose-sensitive coaggregation of the actinomyces with certain plaque streptococci represents another type of adherence involved in microbial colonization. This interaction is mediated by a lectin activity associated with type 2 fimbriae of the actinomyces and a specific carbohydrate- containing antigen present on many streptococcal strains. In other coaggregations which are not lactose-sensitive, a carbohydrate detected on the actinomyces appears to function as a receptor for specific streptococcal lectins. The isolation and structural analysis of various bacterial surface components are being pursued by various approaches including the production of monoclonal antibodies by the hybridoma technique and the application of recombinant DNA technology for the cloning of actinomyces fimbrial genes in Escherichia coli.